This invention relates to the field of animal husbandry and particularly to an improved device for determining when a cow or other animal is in estrus or heat.
Artificial insemination of livestock is being used on an ever increasing scale for selective breeding and to avoid the risks associated with releasing a bull within the herd. Breeding by artificial insemination requires that the semen be administered while the animal is in estrus. The heat cycle is of short duration--from 16 to 24 hours for cattle--and the optimum time for administration of the semen is approximately 12 hours after the onset of the heat cycle.
Various methods have been utilized to identify the onset of estrus in cattle. Most methods are dependent upon the natural homosexual tendencies of the female, manifested by the mounting of the animal in heat by one or more other females. Visual inspection and observation of the herd may of course be employed to identify and segregate females in standing heat, but because of the short duration of the heat cycle, such visual observation must be conducted at least twice daily and accompanied by immediate segregation or marking of the animals to be inseminated. Also, unless the herd is maintained under constant visual observation, the heat cycle may go undetected in many animals. In the dairy industry especially, this failure may be costly, resulting in the loss of at least three weeks milk production amounting to as much as a thousand pounds or more. Optimum ranching practice requires mass breeding of the herd annually so that the animals mature and are ready for market at a common time; visual observation of the herd, which is often widely dispersed, is obviously inefficient.
Various devices and systems have been used or described for improving the efficiency of detection of estrus in bovine herds. U.S. Pat. No. 3,297,020 describes the use of a vaginally inserted electric probe for detecting accelerated mucous secretion accompanying the onset of heat. U.S. Pat. No. 3,844,273 discloses an electronic system comprising radio transmitters individually mounted on the females with switches activated by the mounting animal. U.S. Pat. No. 3,948,249 describes an infra-red temperature detection system for scanning the rump of the female to detect excess warmth caused from repeated mountings. All of these systems are obviously cumbersome at best and require significant capital investment for equipment.
The most successful and widely used type of standing heat detector, of which various forms have been described and used, is a passive device which is glued to the sacrum of the cow in a position to be activated by pressure from the brisket of the mounting animal. Such devices include a reservoir of marker fluid which is discharged in response to pressure to provide a readily observable stain or marking in response to mounting. Such devices are described for example in U.S. Pat. Nos. 3,076,431, 3,158,133, 3,158,134, 3,205,857 and 3,942,475.
Typically, passive standing heat detectors known and used in the art include a reservoir of marker fluid which is compressed by the mounting pressure to discharge some or all of the fluid and provide a telltale marking. The discharge passageway is constricted, or a check valve system provided, to make the device less susceptible to false triggering by a rejected mount or incidental rubbing or brushing of the rump against a tree or barnyard structure. However, the most widely used device (e.g. U.S. Pat. No. 3,075,431) has been found to have inadequate shelf life because of incidental seepage of the marker fluid, while other devices (e.g. U.S. Pat. Nos. 3,158,133, 3,158,134, 3,205,857 and 3,942,475) are undesirably complex and expensive.